There were many mistakes made before the attempt into Stalingrad, all of which being Hitler's. The original plan was good, 6th Army would advance to the Volga, cutting off the Caucasus. Then 4th Panzer Army would advance into the Caucasus capturing the oil fields and encircling any Soviet Armies there.
The first problem was that the Soviets realising they lacked the skill or numbers to face the Wehrmacht in pitched battles just fell back. The German observation of the Allies was that they fought for land instead of over it. The Wehrmacht always aimed to crush the opposition army, not capture land or towns.
Hitler got excited because the 6th Army was advancing with little opposition. He assumed the Soviets lacked any armies that were capable of resistance. He diverted forces from the 6th Army and sent them to join the 4th Panzer Army which he sent to the Caucasus before the trap had been set.
The 6th Army now deprived of vital armour and fuel had to carry on with the original plan, which it in fact achieved. It reached the Volga, cutting off the Caucasus. Then, the critical blow came, Hitler ordered the 6th Army to take Stalingrad! That was never a target for the Wehrmacht didn't care for the cities or towns, they wanted the enemy army!
Then after the realisation that the 6th Army needed more troops, after throwing in it's reserves and not crushing the Soviet bridgehead on the east coast of the Volga, ordered German units on the 6ths' flank to join in, while Romanian, Slovakian and Italian units with no heavy anti-tank artillery took their place!
Then when the Soviets had encircled the 6th Army, they only thought they'd captured 30,000! The 6th Army could have smashed straight through with little effort! 250,000 men would have slaughtered the Soviet troops and just smashed out of the encirclement. But no! Moron Hitler doesn't have a clue and says that 4th Panzer Army is on it's way. In actual fact, the Soviet Armies had pushed further, all the way to Rostov which encircled elements of the 4th Panzer Army and Romanian 3rd Army in Caucasus as well as 6th Army in Stalingrad.
Had Hitler allowed the breakout, Stalingrad would have been the biggest disaster for the Soviets. Instead it was allowed to fester and Goering thought he could deliver 500 tons a day, when 6th Army already said it needed at least 800 tons. Even then, only 80 tons made it everyday. And, by then 7 Soviet Armies had encircled Stalingrad and then the Soviets made a mistake, by attacking Stalingrad instead of letting the German troops to rot!
Out of 100,000 troops captured in Stalingrad, only 6000 returned to Germany.
Wow, that was all off memory...quite a large rant.